This application relates to combustion control systems, and more particularly to dynamic, real time combustion control systems and methods for use with catalytic combustion processes, particularly as they relate to and are utilized by gas turbine engines.
In a conventional gas turbine engine, the engine is controlled by monitoring the speed of the engine and adding a proper amount of fuel to control the engine speed. Specifically, should the engine speed decrease, fuel flow is increased thus causing the engine speed to increase. Similarly, should the engine speed increase, fuel flow is decreased causing the engine speed to decrease. In this case, the engine speed is the control variable or process variable monitored for control.
A similar engine control strategy is used when the gas turbine is connected to an AC electrical grid in which the engine speed is held constant as a result of the coupling of the generator to the grid frequency. In such a case, the total fuel flow to the engine may be controlled to provide a given power output level or to run to maximum power with such control based on controlling exhaust gas temperature or turbine inlet temperature. Again, as the control variable rises above a set point, the fuel is decreased. Alternatively, as the control variable drops below the set point, the fuel flow is increased. This control strategy is essentially a feedback control strategy with the fuel control valve varied based on the value of a control or process variable compared to a set point.
In a typical combustion system using a diffusion flame burner or a simple lean premixed burner, the combustor has only one fuel injector. In such systems, a single valve is typically used to control the fuel flow to the engine. In more recent lean premix systems however, there may be two or more fuel flows to different parts of the combustor, with such a system thus having two or more control valves. In such systems, closed loop control is based on controlling the total fuel flow based on the required power output of the gas turbine while fixed (pre-calculated) percentages of flow are diverted to the various parts of the combustor. The total fuel flow will change over time. In addition, the desired fuel split percentages between the various fuel pathways (leading to various parts of the combustor) may either be a function of certain input variables or they may be based on calculation algorithm using process inputs such as temperatures, airflow, pressures etc. Such control systems offer ease of control due primarily to the very wide operating ranges of these conventional combustors and the ability of the turbine to withstand short spikes of high temperature without damage to various turbine components. Moreover, the fuel/air ratio fed to these combustors may advantageously vary over a wide range with the combustor remaining operational. A wide variety of such control strategies can be employed and a number of these have been described in the literature.
A properly operated catalytic combustion system can provide significantly reduced emissions levels, particularly of NOx. Unfortunately, however, such systems may have a much more limited window of operation compared to conventional diffusion flame or lean premix combustors. For example, fuel/air ratios above a certain limit may cause the catalyst to overheat and lose activity in a very short time. In addition, the inlet temperature may have to be adjusted as the engine load is changed or as ambient temperature or other operating conditions change.
In accordance with one aspect of the invention, there is provided a method of controlling a catalytic combustion system. The catalytic combustion system comprises an air supply, a flame burner, a fuel injector positioned downstream of the flame burner and a catalyst positioned downstream of the fuel injector. A flow path containing a valve directs a portion of the airflow to bypass the catalyst. A portion of the fuel combusts within the catalyst and a remainder of the fuel combusts in the region downstream of the catalyst. The method includes the steps of determining the adiabatic combustion temperature at the catalyst inlet, and adjusting the airflow that bypasses the catalyst to maintain the adiabatic combustion temperature at the catalyst inlet within a predetermined range.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion system. The catalytic combustion system comprises an air supply, a flame burner, a fuel injector positioned downstream of the flame burner and a catalyst positioned downstream of the fuel injector. A flow path containing a valve directs a portion of the airflow to bypass the catalyst. A portion of the fuel combusts within the catalyst and a remainder of the fuel combusts in the region downstream of the catalyst. The method includes the steps of determining the adiabatic combustion temperature at the catalyst inlet, measuring the exhaust gas temperature, calculating the exhaust gas temperature at full load, and adjusting the airflow that bypasses the catalyst to maintain the adiabatic combustion temperature at the catalyst inlet based upon a predetermined schedule. The predetermined schedule relates the i) adiabatic combustion temperature at the catalyst inlet to ii) the difference between the measured exhaust gas temperature and the calculated exhaust gas temperature at full load.
In accordance with yet another aspect of the invention, there is provided a method of controlling a catalytic combustion system. The catalytic combustion system comprises an air supply, a flame burner, a fuel injector positioned downstream of the flame burner and a catalyst positioned downstream of the fuel injector. A flow path containing a valve directs a portion of the airflow to bypass the catalyst. A portion of the fuel combusts within the catalyst and a remainder of the fuel combusts in the region downstream of the catalyst. The method includes the steps of determining the adiabatic combustion temperature at the catalyst inlet, measuring the load, calculating full load, and adjusting the airflow that bypasses the catalyst to maintain the adiabatic combustion temperature at the catalyst inlet based upon a predetermined schedule. The predetermined schedule relates the i) adiabatic combustion temperature at the catalyst inlet to ii) the difference between the measured load and the calculated full load.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion process consisting of a combustion zone through which air is flowed. The process includes a fuel injection means to provide fuel to a catalyst and one or more catalyst sections wherein a portion of the fuel is combusted within the catalyst. The remaining fuel exits the outlet face of the catalyst and combusts in a homogeneous combustion reaction in the space downstream of said catalyst outlet face. The process also includes a bypass system operation that is based on engine output power to maximize the low emissions operating range of said catalyst. The bypass valve closed loop control is based on a flow measuring device.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion process consisting of a combustion zone through which air is flowed. The process includes fuel injection means to provide fuel to a catalyst and one or more catalyst sections wherein a portion of the fuel is combusted within the catalyst. The remaining fuel exits the outlet face of the catalyst and combusts in a homogeneous combustion reaction in the space downstream of said catalyst outlet face. The bypass system operation is based on fundamental engine performance measurements such as exhaust gas temperature, ambient temperature, compressor discharge pressure, and compressor discharge temperature. The bypass valve closed loop control is based on the valve""s feedback position.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion process consisting of a combustion zone through which air is flowed. The process includes a fuel injection means to provide fuel to a catalyst and one or more catalyst sections wherein a portion of the fuel is combusted within the catalyst. The remaining fuel exits the outlet face of the catalyst and combusts in a homogeneous combustion reaction in the space downstream of said catalyst outlet face. A bleed system operation is based on exhaust gas temperature to maximize the low emissions operating range of said catalyst. The bleed valve closed loop control is based on exhaust gas temperature.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion process consisting of a combustion zone through which air is flowed. The process includes a fuel injection means to provide fuel to a catalyst and one or more catalyst sections wherein a portion of the fuel is combusted within the catalyst. The remaining fuel exits the outlet face of the catalyst and combusts in a homogeneous combustion reaction in the space downstream of said catalyst outlet face. A bypass system operation is based on engine output power to maximize the low emissions operating range of said catalyst. A bleed system operation is based on exhaust gas temperature to further increase the low emissions operating range of the catalyst. The bypass valve closed loop control is based on a flow measuring device. The bleed valve closed loop control is based on exhaust gas temperature.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion system comprising a combustor having an air supply, a flame burner, a fuel injector positioned downstream of the flame burner and a catalyst positioned downstream of the fuel injector. A flow path containing a valve directs a portion of the airflow to bypass the catalyst, wherein a portion of the fuel combusts within the catalyst and a remainder of the fuel combusts in the region downstream of the catalyst. The method includes the steps of measuring at least one thermodynamic combustion system parameter, selecting a first predetermined schedule that relates the at least one thermodynamic combustion system parameter to a predetermined airflow that bypasses the catalyst, and controlling the airflow that bypasses the catalyst by selecting the predetermined airflow that bypasses the catalyst from the first predetermined schedule based on the at least one measured thermodynamic combustion system parameter.
In accordance with another aspect of the invention, there is provided a method of controlling a catalytic combustion system comprising a combustor having an air supply, a flame burner, a fuel injector positioned downstream of the flame burner and a catalyst positioned downstream of the fuel injector. A flow path containing a valve bleeds combustor inlet air flow. A portion of the fuel combusts within the catalyst and a remainder of the fuel combusts in the region downstream of the catalyst. The method includes the steps of measuring at least one thermodynamic combustion system parameter, selecting a first predetermined schedule that relates the at least one thermodynamic combustion system parameter to a predetermined airflow that bleeds combustor inlet air flow, and controlling the airflow that bleeds combustor inlet air flow by selecting the predetermined airflow that bleeds combustor inlet air flow from the first predetermined schedule based on the at least one measured thermodynamic combustion system parameter.